o The four basic stages of food processing include: ingestion, digestion, absorption,
o Ingestion is basically feeding – how animals bring food into their digestive tract. There
are four basic ways in which this is performed.
o One way in which this occurs in with suspension feeding (also known as filter feeding) in
which animals filter particles suspended in the water column – only in aquatic animals
(little floating in the air).
o For example, a baleen whale has modified their teeth into baleen (which are comb-like
structures) that takes a big gulp of sea water and forces the water out after filtering out the
krill in the water.
o Sponges also filter feed as water is bathed through their bodies and as it goes through the
choanoderms, the collars of the cell trap suspended particles (debris, microbes in the water,
etc.). Basically, filter the water for the food they need.
o Another form of ingestion is substrate feeding (leaf-minor insect larvae living within the
mesophyll layer of the leaf).
o The leaf – substrate – is its habitat/environment, as it moves through the mesophyll it eats
it and receives the nutrients.
o Therefore, a substrate feeder feeds off of its environment. Another example are
earthworms (they eat the soil they crawl through).
o Fluid feeding also occurs in which animals live almost entirely off of a fluid diet. Aphids
bite into a green plant and suck out the fluid (want the sugar built through photosynthesis).
o Aphids need to eat a lot of the photosynthates to receive enough nutrients in their diet to
sustain them, however, their waste usually has a lot of sugar – honeydew – which is
consumed by ants. o Another example of a fluid feeder is mosquitoes that feed on blood (many organisms do
such as well).
o The most common feeding mechanism for ingestion in the animal kingdom is bulk
feeding. This involves a predator feeding on a prey (whole or in pieces).
o In order for an animal to feed by this mechanism they need to ingest the animal either
whole (daphnia ingested by a hydra – with a modified jaw (anaconda) which can dislocate
on demand) or in pieces.
o For ingestion of chunks of prey to occur the organism needs to have modified teeth to cut
the prey into large pieces (eating animals in chunks and with pieces torn off is the more
derived characteristic – more evolutionarily advantageous to do so).
o The reason why it is evolutionarily advantageous is because a certain prey has a specific
volume with a set number of calories that can be used as fuel. o An animal’s enzymes that work on the prey they swallowed can only work on the surface
of the animal.
o Therefore, physically breaking down the preyinto pieces increases the surface area for the
samevolumethat the animal’s enzymes canprocess andso morecalories canbeobtained.
o Therefore, bulk feeding of pieces of the prey is a much more efficient and advantageous
o It does, however, require adaptation of certain structures to get the whole prey into pieces
(teeth, claws, etc.).
o Mammalian teeth have adaptations depending on the diet they consume.
o The mammalian mouth consists of four main types of teeth:
• Incisors – at the front of the mouth. Tearing small pieces off, nipping small flesh
or plant material
• Canines – fangs, sharp and pointy. Used as a weapon to take down prey
• Premolars – cutting type. Fit together like scissors – “shearing teeth” very good
for cutting meat
• Molars – grinding. Flat surface – come together for effective grinding.
o Each type of teeth has a different structure and so a different function.
o Humans are omnivore (evolved to consume both plant and animal material), we have the
teeth to deal with this adaptation. o Herbivores (animals eatingsolelyplantmaterial),themost important ofthefourteeth types
are the grinding molars which are needed to break down the cell wall material to get to
the nutritious material in the plant cell.
o Therefore, they have large and pronounced molars. At the front, they also have developed
incisors which maybe useful for cutting grass from the ground or leaves from the branches
o Canines aren’t generally required in herbivores, so they are generally reduced (small or
not present). Premolars are also reduced, as they don’t consume flesh to cut and shear.
o Carnivores (animals feeding entirely on other animals – meat) have a different dental
formula. They have very large canines to help the animal in capturing and killing their
o They also have very pronounced premolars (serrated) as they are very sharp and fit
together nicely for the animal to easily tear chunks of meat off of their prey.
o They have very few or no molars as they generally don’t get used (as most carnivores
simplytear off a chunk of flesh and swallow it – theydo not spend much time chewing and
grinding their food). o Chewing is the first stage of digestion (mechanical digestion) where large objects are
broken down, torn or grinded into smaller pieces (the molecular structures of the food is
o Chemical digestion involves the breaking of bonds between atoms in the molecules that
is consumed. Chemical digestion can occur within the cell (in vesicles – intracellular
o Sponges rely entirely on intracellular digestion within the choanocytes. Food particles in
the water are filtered and enter the cell through vesicles where they are broken down.
o All other animals have some quantity of intracellular digestion (humans break down
tripeptides within cells). Every other organism in the animal kingdom also has
o For example, the daphnia is digested in the gastrovascular cavity (chamber) of the hydra.
This occurs via enzymes that are dumped into the gastrovascular cavity, which break down
the macromolecules of the food into monomers that are absorbed by the cells. Still some
intracellular digestion occurs.